1. Field of the Invention
The present invention relates to a motor-powered opening/closing apparatus for a window or door and, more particularly, to a motor-powered opening apparatus suitable as an automobile power window apparatus.
2. Description of the Prior Art
In a conventional automobile power window motor driver, a motor is stopped in response to outputs from sensors such as limit switches for detecting ascending and descending ends of a window glass. Another conventional motor driver uses an overcurrent detection/timer circuit or an overcurrent limiter circuit in place of an end position sensor to cut off or limit a drive current when the motor is stopped or becomes in a constrained state.
In power window motor stop control using a limit switch, a constraining current is continuously supplied to the motor while part of a driver or passenger body is clamped between a glass and a window frame during upward driving of the window glass. Therefore, the driver or passenger may be hurt.
The overcurrent detection/timer circuit or the overcurrent detection limiter circuit primarily aims at detecting an increase in torque on the basis of a constraining current. Therefore, a large torque is generated until or even after a completely constrained state is set. If a soft object such as a child body is clamped between the window glass and the window frame, the limiter circuit may not immediately respond to stop the motor.
Since the conventional detection arrangements are based on current detection, they tend to be adversely affected by variations in power source voltage. Circuit breaking or torque limiting cannot be accurately performed. In particular, when a voltage level is decreased, a constraining current of level lower than a detection level may continuously flow.
In order to solve the above problem, a pressure sensor may be arranged on a glass contact surface of an upper window frame in an automobile. When the window glass reaches the upper end or a foreign object is clamped between the window glass and the window frame, the motor may be stopped in response to an output from the pressure sensor.
However, if sensitivity of the pressure sensor is improved to prevent an accident as described above, slight distortion of the window frame which is caused by deterioration over time may cause incomplete closing of the window glass. In order to prevent this, the sensitivity level of the pressure sensor must be lowered to allow complete closing of the window glass with a sufficient pressure. In this case, the pressure sensor does not respond to clamping of a body portion between the window glass and the window frame.